(HealthScoutNews) -- A woman who experiences major stressful events between the 24th and 28th weeks of pregnancy has a dramatically increased risk of giving birth to a child with autism, new research says.

"These are major stressors we are talking about, like the death of a loved one, the loss of a job or something extremely traumatic that occurs specifically during these weeks of the pregnancy," says lead study author Dr. David Beversdorf, assistant professor of neurology at Ohio State University Medical Center.

Could the terrorist attacks of Sept. 11 be among such major stressors? Beversdorf says yes, but not for every woman.

"It depends on how each individual woman reacts to stress during her pregnancy, what her level of stress was prior to becoming pregnant, what it was during the pregnancy and what upsets her personally the most," Beversdorf says.

Dr. Michael Paidas, director of the program of maternal-fetal medicine at New York University Medical Center, says the study is significant but that all women, particularly New York City women, shouldn't be frightened -- or stressed -- by the finding.

"There is so much human biologic variability that occurs that to be able to say that we are going to see some structural change [in the baby] and then say that this is related exactly to autism is going to be a stretch," says Paidas.

However, he says the findings are important, meshing with other research showing that stress can affect pregnancy, including increasing the risk of premature delivery.

"I think we are just beginning to learn about the role of stress in pregnancy, and as time goes on, we will be better able to define what the true links are," says Paidas.

Beversdorf says one link may be hormone-related, specifically hormones like cortisol whose levels rise in the mother's body in direct response to extremely stressful events. He says a biochemical chain reaction may occur during a specific time in the pregnancy and may interfere with the development of the cerebellum, an area of the brain that is structurally different in children with autism.

This idea is supported by animal data suggesting that stress during a specific time in a pregnancy causes structural changes in the brain of the developing offspring similar to what is seen in autistic children.

"It's clear that there is a definite genetic component to autism, but the condition is such that genes alone cannot explain away the whole reason why autism exists," says Beversdorf. Maternal stress may be one of the missing links, he says.

Autism is a neurological disorder that can dramatically affect behavior patterns and the ability to communicate.

Beversdorf's study involved questionnaires that asked mothers to document extremely stressful events during their pregnancies. Researchers say they defined "extremely stressful" as any life-altering event, such as the death of a loved one, a divorce or a job loss.

The study included 188 women who had given birth to autistic children, 212 women who had normal children and 92 women who had given birth to babies with Down's syndrome.

The first result: The numbers of women experiencing major stress during any four-week period of their pregnancies were pretty much the same among both the mothers of normal babies and mothers of Down's syndrome babies. However, the stress levels for mothers of autistic children were nearly twice that of the other mothers in the study.

"First we thought that a woman who had an autistic child may simply be more likely to remember stressful events more readily than a woman who gave birth to a normal child," says Beversdorf. But continued analysis proved more than just chance was involved.

The second result: The stressful events always happening between the 24th and 28th week of pregnancy.

"It was clear there was something going on here. The stressors were all taking place during specific times in the pregnancy, and this time coincides with the development of an area of the brain that has already been linked to autism, so it was hard not to see the links," Beversdorf says.

The findings were presented at last month's annual meeting of the Society for Neuroscience, in San Diego.

Paidas says the findings are interesting, but he says it's premature to say for certain that stress is the culprit behind the autistic births.

"Stress is important, and we are now finding some biochemical links and outcomes. But this is still very preliminary and only one facet of stress. And each individual person does have their own coping mechanisms and their own way of dealing with stress, both psychologically and biochemically. So, it's difficult to draw any definite conclusions based on just one study," says Paidas.

What To Do

Based on existing research, Paidas says women should not be overly concerned about stressful events beyond their control that might occur during their pregnancy.

"One thing we know for sure: Worrying about the effects of stress will cause more stress. So, if something stressful occurs at any time during your pregnancy, don't panic, but do bring it to the attention of your obstetrician," says Paidas.

For more information on autism, visit the Autism Society of America. To learn more about the effects of stress on the body, click here. For information on how stress can affect a pregnancy, click here.

For tips on how to reduce stress, visit the National Mental Health Association.

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